Mitigation of seismic waves using graded broadband metamaterial

In recent years, researchers have shown interest in blocking low-frequency vibrations with the aid of metamaterials due to their inherent wave-filtering properties. However, proposing a practical metamaterial layout remains a challenge, taking into consideration the size, shape, and availability of metamaterial components. This study proposes a new configuration that can increase the range of the attenuation frequency. The configuration focuses on the capability of graded metamaterials in filtering a wide range of wave frequencies that can be generated by low-amplitude waves. To find the best configuration with the widest bandgap, square periodic sections using different materials including steel, rubber, concrete, tungsten, and carbon fiber-reinforced polymer were considered. Unit cells with two layers of materials were examined numerically to determine the attenuation zones and the effect of material properties and core size on the bandgap width and frequency range. Furthermore, the performance of the unit cells in a soil medium under the low-amplitude low-frequency surface and bulk waves is evaluated in the frequency domain using finite element analysis, in which the metamaterial is embedded periodically in a soil medium with different configurations, including a graded distribution. The results show that having an array of unit cells spaced periodically can decrease the transmission of the wave to the protected zone located after the array, and the application of grading can increase the attenuation zones to filter frequencies as low as 4.5 Hz and up to 29 Hz.